I think at least some of the problem with IK in Poser is in the way the joints are set up on the models. Unlike other apps, which often use a much more sophisticated means of rigging characters, Poser uses rather primitive falloff zone joints which don't really provide superior control over the way body parts bend or move in the hierarchy. I imagine this can affect the way IK behaves as well.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.